In Three-Dimensional Integrated Circuits (3DIC), devices dies are either bonded on interposers, package substrates, or stacked on other device dies. Although the performance of the respective circuits is improved, the heat dissipation becomes a more significant concern. Conventionally, the heat in device dies is dissipated to the overlying heat sink through a Thermal Interface Material (TIM) layer, which adheres the heat sink to the underlying device dies. The thermal conductivity of the TIM, however, is not satisfactory. Hence, the heat dissipation through the TIM becomes a bottle neck for improving the heat dissipation.